The present invention relates to a method for drivingly controlling a variable reluctance type motor, and more particularly, to a drive control method of this kind capable of improving the efficiency of a motor.
A variable reluctance type motor, which comprises a stator having a plurality of salient poles around which windings are wound and a rotor having a plurality of salient poles, is so arranged as to rotate the rotor by attracting a rotor salient pole near an excited stator salient pole towards the stator salient pole by a magnetic attraction force caused by the excited stator salient pole. At this time, the rotary torque applied to the rotor acts in a direction to reduce the magnetic resistance between the stator salient pole and the rotor salient pole, irrespective of the direction of a current flowing in the stator winding. That is, during the rotor rotation, the rotary torque acting in the direction of the rotor rotation is applied to the rotor from an instant at which the rotor salient pole starts to face the excited stator salient pole (unalign position) until an instant at which the rotor salient pole is brought to completely face the stator salient pole (align position). Thereafter, when the rotor further continues to rotate in the same direction, the rotary torque acting in a direction opposite to the rotation direction of the rotor is applied to the rotor salient pole until the rotor salient pole starts to be deviated from a state where it faces the stator salient pole.
For example, in case that the rotor 21 rotates in a counterclockwise direction relative to the stator 20 as shown in FIGS. 4A and 4B, the rotary torque acting in the rotor rotation direction or the counterclockwise direction is applied to a rotor salient pole 21a from the time when the leading edge 21a', as viewed in the rotor rotation direction, of the rotor salient pole 21a has reached a position on an extension of the leading edge 20A' of an excited stator salient pole 20A of A-phase and hence the rotor salient pole 21a has reached that rotary position unalign position (electrical angle of 0 degree) of the rotor which is shown in FIG. 4A at which it starts to face the stator salient pole 20A until the time at which the rotor salient pole 21a has reached a rotor rotary position align position (electrical angle of 180 degrees) shown in FIG. 4B at which it completely faces the stator salient pole 20A, with the axes of the rotor salient pole 21a and the stator salient pole 20A brought to be coincide with each other. When the rotor 21 continues to further rotate in the counterclockwise direction after having reached the rotor rotation position shown in FIG. 4B, the rotary torque acting in a direction opposite to the rotor rotation direction or the clockwise direction is applied to the rotor salient pole 21a until the trailing edge 21a" of the rotor salient pole 21a reaches a position on the extension unalign position (again) (electrical angle of 360 degrees) of the trailing edge 20A" of the stator salient pole 20A and hence the rotor salient pole 21a starts to be deviated from a state where it faces the stator salient pole 20A. At the time of releasing from the state where the rotor salient pole 21a faces the stator salient pole 20A, the leading edge 21d' of the next rotor salient pole 21d reaches a position on the extension of the leading edge 20A' of the stator salient pole 20A, so that the rotor salient pole 21d starts to face the stator salient pole 20A.
After all, the acting direction of the rotary torque caused when a stator salient pole of a certain phase is excited is determined in dependence on the rotary position (electrical angle) of the rotor representing the positional relation between the stator salient pole and the rotor salient pole. Thus, in order to cause the variable reluctance type motor to rotate in a desired direction, the respective stator salient poles are sequentially excited in a desired order for a desired period of time in accordance with the rotary position of the rotor. For example, in an example shown in FIGS. 4A and 4B, if the rotor 21 is to be rotated counterclockwise, an A-phase stator winding (not shown) wound around the stator salient pole 20A is energized in a rotor rotation region represented by an electrical angle region of 0 to 180 degrees. On the other hand, in the case of rotating the rotor 21 clockwise, the A-phase stator winding is energized in a rotor rotation region indicated by an electrical angle region of 180 to 360 degrees. Conventionally, in order to control the drive of the variable reluctance type motor, data is read out from a read only memory, in which the above two types of excitation patterns are previously stored, in accordance with the rotary position of the rotor, so that the stator windings of respective phases are each energized in a desired order for a desired period of time.
However, due to the presence of an inductance of the stator winding, a current continues to flow in the winding for a certain period of time after excitation of the stator winding is interrupted. For example, in a case where the A-phase stator winding is energized for an excitation section T1 corresponding to an electrical angle region of 0 to 180 degrees of the rotor in order to rotate the rotor 21 in the counterclockwise direction, a current will flow in the stator winding even in a section T2 corresponding to rotor electrical angle positions which exceed 180 degrees, as shown in FIG. 5. As a result, a disturbance torque acting to rotate the rotor in a direction opposite to the desired rotation direction is generated. Hence, energy is consumed to cancel the disturbance torque, so that the motor efficiency will be lowered.